U.S. patent application number 12/412704 was filed with the patent office on 2009-10-01 for electronic device, detection circuit and voltage control method.
This patent application is currently assigned to FUJITSU MICROELECTRONICS LIMITED. Invention is credited to Mayo Kitano, Masatoshi Kokubun, Takashi Matsumoto.
Application Number | 20090243576 12/412704 |
Document ID | / |
Family ID | 41116105 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090243576 |
Kind Code |
A1 |
Kitano; Mayo ; et
al. |
October 1, 2009 |
ELECTRONIC DEVICE, DETECTION CIRCUIT AND VOLTAGE CONTROL METHOD
Abstract
A voltage control method includes producing an error signal
based on a difference between a reference signal and an adaptor
voltage and an adaptor current corresponding to the adaptor
voltage, regulating, based on the error signal, the adaptor
voltage, comparing a reference voltage to a voltage proportional to
a potential corresponding to an identifying voltage corresponding
to the adaptor voltage, detecting, based on the comparison result,
whether or not a couplable external power source is suitable, and
setting based, on the detection result, a potential corresponding
to the identifying voltage.
Inventors: |
Kitano; Mayo; (Kasugai,
JP) ; Kokubun; Masatoshi; (Kasugai, JP) ;
Matsumoto; Takashi; (Kasugai, JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU MICROELECTRONICS
LIMITED
Tokyo
JP
|
Family ID: |
41116105 |
Appl. No.: |
12/412704 |
Filed: |
March 27, 2009 |
Current U.S.
Class: |
323/282 |
Current CPC
Class: |
H02J 7/34 20130101; H02M
3/156 20130101 |
Class at
Publication: |
323/282 |
International
Class: |
G05F 1/00 20060101
G05F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2008 |
JP |
2008-091405 |
Feb 6, 2009 |
JP |
2008-026519 |
Claims
1. An electronic device comprising: a system circuit operating
based on an adaptor voltage which is input to a power source
terminal; and a detection circuit detecting the adaptor voltage and
an adaptor current corresponding to the adaptor voltage by a
resistor coupled between the power source terminal and the system
circuit, wherein the detection circuit comprises: an error
amplifier outputting an error signal corresponding to a difference
between the adaptor voltage and a reference signal; a current
control circuit coupled to a control terminal through which an
identifying voltage is input and outputting, based on the error
signal, a control current corresponding to the adaptor voltage; a
monitoring circuit coupled to the control terminal, comparing a
reference voltage with a voltage corresponding to a potential of
the control terminal based on the identifying voltage, and
producing, based on a result of the comparison, a detection signal
indicating whether or not an external power source connected to the
power source terminal is suitable; a switch control circuit turning
on/off, based on the detection signal a switch coupled between the
power source terminal and the resistor; and a setting circuit
setting the potential of the control terminal.
2. The electronic device according to claim 1, wherein the setting
circuit is a constant current circuit coupled to the control
terminal and supplying a constant current to the control
terminal.
3. The electronic device according to claim 1, wherein the setting
circuit is coupled between the error amplifier and the current
control circuit, receives the detection signal, and clamps the
potential of the control terminal through the current control
circuit to the adaptor voltage based on the detection signal.
4. The electronic device according to claim 3, wherein the current
control circuit comprises a first MOS transistor including a drain
coupled to the control terminal, a source receiving the adaptor
voltage, and a gate coupled to a current-voltage conversion
circuit; and the current-voltage conversion circuit that supplies a
voltage proportional to the error signal produced by the error
amplifier to the gate of the first MOS transistor, wherein the
current-voltage conversion circuit comprises a second MOS
transistor coupled in current-mirror form to the first MOS
transistor, a third MOS transistor coupled in series to the second
MOS transistor, and a resistor, and wherein the setting circuit is
coupled between the error amplifier and a gate of the third MOS
transistor, and when the detection signal is at a first level,
transmits the error current produced by the error amplifier to the
gate of the third MOS transistor, or when the detection signal is
at a second level, cuts off the transmission of the error current
and keeps the gate voltage of the third MOS transistor at the time
of the cutoff.
5. The electronic device according to claim 3, wherein the current
control circuit comprises a first MOS transistor having a drain
coupled to the control terminal, a source receiving the adaptor
voltage, and a gate coupled to a current-voltage conversion
circuit; and the current-voltage conversion circuit that supplies a
voltage proportional to the error signal produced by the error
amplifier to the gate of the first MOS transistor, wherein the
current-voltage conversion circuit comprises: a second MOS
transistor coupled in current-mirror form to the first MOS
transistor; a third MOS transistor coupled in series to the second
MOS transistor; and a resistor, and wherein the setting circuit is
coupled between the error amplifier and the gate of the third MOS
transistor, and when the detection signal is at a first level,
transmits the error current produced by the error amplifier to the
gate of the third MOS transistor, or when the detection signal is
at a second level, cuts off the transmission of the error current
and supplies the adaptor voltage to the gate voltage of the third
MOS transistor.
6. The electronic device according to claim 1, wherein the main
device is coupled to a secondary battery producing a battery
voltage, wherein the system circuit operates using at least one of
the adaptor voltage and the battery voltage, wherein the detection
circuit detects the battery voltage and a battery current
corresponding to the battery voltage by use of a resistor coupled
between the battery and the system circuit, wherein the error
amplifier produces an error signal based on a difference between
the reference signal and at least two of the adaptor voltage, the
adaptor current, the battery voltage, and the battery current, and
wherein the switch control circuit turns on/off, based on the
detection signal, a first switch coupled between the power source
terminal and the resistor and a second switch coupled between the
resistor used to detect the battery current and the battery.
7. A detection circuit comprising: an error amplifier outputting an
error signal based on a difference between an adaptor voltage and
an adaptor current based on the adaptor voltage and a reference
signal; a current control circuit outputting, based on the error
signal, a control current corresponding to the adaptor voltage; a
monitoring circuit comparing a reference voltage with a voltage
proportional to a potential based on an identifying voltage
corresponding to the adaptor voltage, and producing, based on a
result of the comparison, a detection signal indicating whether or
not a coupled external power source is suitable; a switch control
circuit turning on/off, based on the detection signal, a switch
coupled between the power source terminal and a resistor; and a
setting circuit setting a potential based on the identifying
voltage.
8. The detection circuit according to claim 7, wherein the setting
circuit is a constant current circuit that supplies a constant
current.
9. The detection circuit according to claim 7, wherein the setting
circuit is coupled between the error amplifier and the current
control circuit, receives the detection signal, and clamps, based
on the detection signal, a potential corresponding to the
identifying voltage through the current control circuit to the
adaptor voltage.
10. The detection circuit according to claim 7, wherein the
detection circuit is coupled to a secondary battery producing a
battery voltage and to a system circuit that operates using at
least one of the adaptor voltage and the battery voltage, wherein
the detection circuit detects the battery voltage and a battery
current corresponding to the battery voltage by use of a resistor
coupled between the battery and the system circuit, wherein the
error amplifier produces an error signal based on a difference
between the reference signal and at least two of the adaptor
voltage, the adaptor current, the battery voltage, and the battery
current, and wherein the switch control circuit turns on/off, based
on the detection signal, a first switch coupled between the power
source terminal and the resistor and a second switch coupled
between the resistor used to detect the battery current and the
battery.
11. A voltage control method comprising: producing an error signal
based on a difference between a reference signal and an adaptor
voltage and an adaptor current corresponding to the adaptor
voltage; regulating, based on the error signal, the adaptor
voltage; comparing a reference voltage to a voltage proportional to
a potential corresponding to an identifying voltage corresponding
to the adaptor voltage; detecting, based on the comparison result,
whether or not a couplable external power source is suitable; and
setting based, on the detection result, a potential corresponding
to the identifying voltage.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2008-091405,
filed on Mar. 31, 2008 and the prior Japanese Patent Application
No. 2009-026519, filed on Feb. 6, 2009, the entire contents of
which are incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein are related to an
electronic device, a detection circuit, and a voltage control
method.
BACKGROUND
[0003] Typical electronic devices are provided with a secondary
battery as a drive power source. Such electronic devices include a
charging circuit for charging the secondary battery using a
charging current supplied from an external power source.
[0004] It is desirable that the main unit of an electronic device
be able to control an AC adaptor to regulate the output voltage
supplied from the AC adaptor to the main device. In this case, the
AC adaptor includes a voltage regulating circuit, and a detection
circuit included in the main device detects a voltage or the like
to produce a control signal for controlling the voltage regulating
circuit. Furthermore, since the main device needs to detect whether
or not the coupled AC adaptor is suitable for the device, the AC
adaptor outputs information identifying the AC adaptor to the main
device. For example, the detection circuit of the main device
monitors a voltage of the coupling terminal and determines whether
or not the coupled AC adaptor is suitable for the device. The main
device may not control an AC adaptor which is not suitable for the
device, so the main device turns off a switch disposed in the power
supply path to protect system circuits and the like of the main
device.
[0005] In the above electronic device, the AC adaptor is coupled to
the main device via, for example, a DC plug 90 illustrated in FIG.
1. In the DC plug 90, a cylindrical power terminal 92 is formed in
the outer circumference surface of a cylindrical insulator 91; a
cylindrical ground terminal 93 is formed in the inner circumference
surface of the insulator 91; and a rod-like control terminal 94 is
arranged at the axial center of the insulator 91. The length of the
control terminal 94 is set shorter than the lengths of power
terminal 92 and ground terminal 93 in a direction of inserting the
DC plug 90. That is, the tip ends of the power terminal 92 and
ground terminal 93 protrude further relative to the tip end of the
control terminal 94. The AC adaptor outputs an identification
signal via the control terminal 94 to the main device; and the main
device outputs a control signal via the control terminal 94 to the
AC adaptor.
[0006] As depicted in FIG. 1, the ground terminal 93 and power
terminal 92, and then the control terminal 94 are electrically
coupled in order to terminals of the main device. With this
configuration, the signal (information) is supplied to the
detection circuit of the main device after supplying the power
supply voltage. Thus, in case the DC plug 90 coupled to the AC
adaptor after the AC plug has been inserted in an AC outlet is
coupled to the main device, the main device is prevented from being
damaged. Such configuration in which coupling of the control
terminal 94 is done after coupling of the power terminal 92 and
ground terminal 93 is used not only by the DC plug 90 having this
shape but also by a DC plug having another shape.
[0007] As further depicted in FIG. 1, in the above electronic
device, during a period from coupling of the power terminal 92 and
ground terminal 93 of the DC plug 90 to coupling of the control
terminal 94, the terminal of the main device to be coupled to the
control terminal is still not coupled. As a result, the potential
of the terminal of the main device may become unstable, causing a
malfunction.
SUMMARY
[0008] According to an aspect of the embodiments, a voltage control
method includes producing an error signal based on a difference
between a reference signal and an adaptor voltage and an adaptor
current corresponding to the adaptor voltage, regulating, based on
the error signal, the adaptor voltage, comparing a reference
voltage to a voltage proportional to a potential corresponding to
an identifying voltage corresponding to the adaptor voltage,
detecting, based on the comparison result, whether or not a
couplable external power source is suitable, and setting based, on
the detection result, a potential corresponding to the identifying
voltage.
[0009] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0010] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and/or other aspects and advantages will become
apparent and more readily appreciated from the following
description of the embodiments, taken in conjunction with the
accompanying drawings of which:
[0012] FIG. 1 illustrates a cross-sectional view of an exemplary DC
plug;
[0013] FIG. 2 illustrates an aspects of an electronic device
related to an embodiment;
[0014] FIG. 3 illustrates an aspect of the AC adaptor in FIG.
2;
[0015] FIG. 4 illustrates an aspect of the main device in FIG.
2;
[0016] FIG. 5 illustrates an aspect of the voltage control circuit
in FIG. 4;
[0017] FIG. 6 illustrates a timing chart of an aspect of the
operation of the voltage control circuit in FIG. 4;
[0018] FIG. 7 illustrates a timing chart of an aspect the operation
of the voltage control circuit in FIG. 4;
[0019] FIG. 8 illustrates another aspect of the voltage control
circuit in FIG. 4;
[0020] FIG. 9 illustrates another aspect of the voltage control
circuit in FIG. 4; and
[0021] FIG. 10 illustrates another aspect of the voltage control
circuit in FIG. 4.
DESCRIPTION OF EMBODIMENTS
[0022] An embodiment will be described below with reference to
FIGS. 2 to 7.
[0023] As shown in FIG. 2, an AC adaptor 21 acting as an external
power source is coupled to a main device 31. The AC adaptor 21 is
coupled to an AC power source, and commercial AC voltage supplied
from the AC power source is input to a voltage conversion circuit
22 of the AC adaptor 21. The voltage conversion circuit 22 converts
an AC voltage into a DC voltage and outputs the DC voltage. A
voltage control circuit 23, which receives control current Isc, has
a function of producing, based on the control current Isc, a
regulated adaptor voltage VAC from the DC voltage. The AC adaptor
21 is coupled to the main device 31 via, for example, the DC plug
90 illustrated in FIG. 1, and supplies the produced adaptor voltage
VAC to the main device 31. The voltage control circuit 23 further
has a function of outputting, as an identifying voltage, a power
limiting signal PWRM having a voltage value dependent on power
information of the AC adaptor 21.
[0024] As further shown in FIG. 2, the adaptor voltage VAC is
supplied via a resistor R1 to a system DC/DC converter 32. Coupled
via a resistor R2 to the system DC/DC converter 32 is a secondary
battery ("battery" for short) BT. The system DC/DC converter 32
produces, based on the adaptor voltage VAC and a battery voltage
supplied from the battery, a system voltage VS obtained by voltage
conversion of an input voltage and supplies the system voltage VS
to a system circuit 33. Consequently, a power dependent on at least
one of the power supplied from the AC adaptor 21 and the power
supplied from the battery BT is supplied to the system circuit 33.
The system circuit 33 is a circuit that provides various types of
functions of the main device 31.
[0025] As further shown in FIG. 2, the battery detection circuit 34
of the main device 31 includes one or more semiconductor devices.
The semiconductor device includes a chip and/or a package including
the chip. The battery detection circuit 34 is coupled to both
terminals of the resistor R1 and coupled between the resistor R2
and battery BT. The battery detection circuit 34 detects based on a
voltage across the resistor R1, current (adaptor current) lout
flowing in the resistor R1. Also, the battery detection circuit 34
detects, based on a voltage across the resistor R2, current
(battery current) Ichg flowing in the resistor R2. Furthermore, the
battery detection circuit 34 detects a voltage (or an adaptor
voltage VAC) supplied to the system DC/DC converter 32 and detects
a terminal voltage of the battery BT. The battery detection circuit
34 produces a control current Isc based on the detected voltage and
current, and on a power limiting signal PWRM supplied from the AC
adaptor 21. The control current Isc is supplied to the voltage
control circuit 23 of the AC adaptor 21. Consequently, the voltage
control circuit 23 of the AC adaptor 21 regulates adaptor voltage
VAC according to the control current Isc output from the battery
detection circuit 34.
[0026] As further shown in FIG. 2, the battery detection circuit 34
determines, based on a voltage of the control terminal to which
power limiting signal PWRM is supplied, whether or not an AC
adaptor is suitable for supplying power to the main device 31. An
appropriate AC adaptor has a control terminal and has a function of
regulating its output voltage in response to control current Isc
output from the battery detection circuit 34, whereas an
inappropriate AC adaptor does not regulate its output voltage.
Determining that the AC adaptor coupled is appropriate, the battery
detection circuit 34 supplies power supplied from the AC adaptor to
the system DC/DC converter 32 and also charges the battery BT using
the power. Meanwhile, when the battery detection circuit 34
determines that the AC adaptor coupled is inappropriate, the
battery detection circuit 34 does not supply power supplied from
the AC adaptor to the system DC/DC converter 32 and the battery
BT.
[0027] An exemplary configuration of the AC adaptor 21 will be
described with reference to FIG. 3.
[0028] As illustrated in FIG. 3, an output terminal of the voltage
conversion circuit 22 is coupled to a first terminal (for example,
source) of a first transistor T11; a second terminal (for example,
drain) of the first transistor T11 is coupled to a first terminal
of a choke coil L1; and a second terminal of the choke coil L1 is
coupled to a first terminal P1 acting as a power source terminal.
The second terminal of the first transistor T11 is also coupled to
a first terminal (for example, drain) of a second transistor T12; a
second terminal (for example, source) of the second transistor T12
is coupled to the ground. A control terminal (gate) of the first
transistor T11 and a control terminal (gate) of the second
transistor T12 are coupled to a pulse width modulator (PWM) 24.
According to the present embodiment, the first transistor T11 is a
p-channel MOS transistor; and the second transistor T12 is an
n-channel MOS transistor. FIG. 3 also illustrates body diodes of
the transistors T11 and T12.
[0029] A first terminal of the choke coil L1 is coupled to the
cathode of the diode D1; and the anode of the diode D1 is coupled
to the ground. The first terminal P1 is coupled to a first terminal
of a smoothing capacitor C1; and a second terminal of the capacitor
C1 is coupled to the ground. A second terminal P2 acting as a power
source terminal is coupled to the ground; and a third terminal P3
acting as a control terminal is coupled to the pulse width
modulator (PWM) 24. Input via the third terminal P3 to the pulse
width modulator 24 is control current Isc. According to the present
embodiment, the pulse width modulator 24 outputs, via the third
terminal P3, a power limiting signal PWRM having a voltage
dependent on power information of the AC adaptor 21.
[0030] As further illustrated in FIG. 3, the pulse width modulator
(PWM) 24 performs on/off control of the first transistor T11 and
second transistor T12 alternately using a given duty cycle. The
output current of the transistor T11 is smoothed by the choke coil
L1 and capacitor C1 due to the switching operation of the first
transistor T11. In this case, when the first transistor T11 is in
an ON state, the output voltage of the voltage conversion circuit
22 is supplied via the transistor T11 to an LC circuit (smoothing
circuit including the choke coil L1 and capacitor C1). When the
first transistor T11 is turned OFF and the second transistor T12 is
turned ON, a current path is formed. Then, energy accumulated in
the choke coil L1 when the first transistor T11 is in an ON state
is discharged to the first terminal P1 side.
[0031] Furthermore, the pulse width modulator 24 modifies the duty
cycle in response to control current Isc. For example, the pulse
width modulator 24 modifies the duty cycle to vary the ON period of
the first transistor T11 according to the value of control current
Isc. An adaptor voltage VAC output from the AC adaptor 21
corresponds to the ON period of the first transistor T11. As the ON
period of the first transistor T11 increases, the energy
accumulated in the choke coil L1 becomes larger, so a higher
adaptor voltage VAC is output. As the ON period of the first
transistor T11 decreases, the energy accumulated in the choke coil
L1 becomes smaller, so a lower adaptor voltage VAC is output.
[0032] The first terminal P1 and second terminal P2 are coupled to
a first terminal P11 and second terminal P12, respectively,
illustrated in FIG. 4; and the third terminal P3 is coupled to a
third terminal P13 illustrated in FIG. 4.
[0033] A configuration of the main device 31 will be described with
reference to FIG. 4.
[0034] As illustrated in FIG. 4, the first terminal P11 acting as a
power source terminal is coupled to the battery detection circuit
34 and a first terminal of a switch SW1. The second terminal P12
acting as a power source terminal is coupled to the ground. The
third terminal P13 acting as a control terminal is coupled to the
battery detection circuit 34.
[0035] As further illustrated in FIG. 4, a second terminal of the
switch SW1 is coupled to the battery detection circuit 34 and a
first terminal of a switch SW2. A second terminal of the switch SW2
is coupled to a first terminal of the resistor R1, and a second
terminal of the resistor R1 is coupled to the system DC/DC
converter 32 (refer to FIG. 2) and a first terminal of the resistor
R2. A second terminal of the resistor R2 is coupled to a first
terminal of a switch SW3, a second terminal of the switch SW3 is
coupled to a positive terminal of the battery BT, and a negative
terminal of the battery BT is coupled to the ground.
[0036] The switches SW1 to SW3 are each an analog switch including
a p-channel MOS transistor, for example, and their control
terminals are coupled to the battery detection circuit 34. The
switches SW1 to SW3 turn ON or OFF in response to control signals
SC1 to SC3 supplied from the battery detection circuit 34. Some of
the circuits included in the battery detection circuit 34 operate
on power supply from the battery BT to turn ON/OFF switches SW1 to
SW3 when a given adaptor voltage VAC is not supplied via the first
terminal P11, that is, when the AC adaptor 21 is not coupled. In
the present embodiment, some circuits included in the battery
detection circuit 34 at least control the ON/OFF of the third
switch SW3. Consequently, the system circuit 33 illustrated in FIG.
2 may operate using the system voltage VS supplied via the system
DC/DC converter 32 from the battery BT.
[0037] However, when the adaptor voltage VAC produced by the AC
adaptor 21 illustrated in FIG. 3 is supplied via the first terminal
P11, some circuits included in the battery detection circuit 34
operate using the adaptor voltage VAC. When the adaptor voltage VAC
of a given value or more is supplied, the operating circuits turn
ON the first switch SW1. As a result, the adaptor voltage VAC is
supplied as drive voltage VDC via the first switch SW1 to the
battery detection circuit 34. Many circuits included in the battery
detection circuit 34 operate using the drive voltage VDC to
regulate adaptor voltage VAC, charge the battery BT, and perform
other operations.
[0038] As further illustrated in FIG. 4, both terminals of the
resistor R1 are coupled to input terminals of a current amplifier
41 of the battery detection circuit 34; and both terminals of the
resistor R2 are coupled to input terminals of a current amplifier
42. The current amplifier 41 detects current Iout flowing in the
resistor R1, that is, an output current of the AC adaptor 21, and
outputs a current detection signal S1 corresponding to the
detection result to an error amplifier 43 acting as a differential
amplifier. The current amplifier 42 detects current Ichg flowing in
the resistor R2, that is, charge current Ichg flowing to the
battery BT, and outputs charging current detection signal S2
corresponding to the detected current to the error amplifier
43.
[0039] As further illustrated in FIG. 4, the error amplifier 43
includes two inverted input terminals and one non-inverted input
terminal. In the error amplifier 43, the current detection signal
S1 is input to the first inverted input terminal, and charging
current detection signal S2 is input to the second inverted input
terminal. Input to the non-inverted input terminal of the error
amplifier 43 is a reference signal based on current reference
signal IOUTM and limiting current signal IDAC. The current
reference signal IOUTM is set according to the total amount of
current used in the main device 31; and the limiting current signal
IDAC is set to a voltage set according to the charging current of
the battery BT. The error amplifier 43 compares the reference
signal with the larger of the current detection signal S1 and
charging current detection signal S2, and produces an error voltage
dependent on the comparison result.
[0040] As further illustrated in FIG. 4, a coupling point between
the resistor R2 and the battery BT is coupled to an inverted input
terminal of an error amplifier 44. A voltage limiting signal VDAC
is input to a non-inverted input terminal of the error amplifier
44. The error amplifier 44 amplifies a difference between a
terminal voltage of the battery BT and voltage limiting signal VDAC
to produce an error voltage.
[0041] As further illustrated in FIG. 4, both terminals of the
resistor R1 are coupled to a multiplier 45. The multiplier 45
detects the terminal voltage across the resistor R1, that is, the
drive voltage VDC, and also detects the total amount of current
from the voltage across the resistor R1. Then, the multiplier 45
multiplies the drive voltage VDC by the total amount of current to
obtain a power detection signal PWRO, and outputs the power
detection signal PWRO to an error amplifier 46. In the error
amplifier 46, the power detection signal PWRO is input to an
inverted input terminal of the error amplifier 46, and a power
limiting signal PWRM is input to the non-inverted input terminal
the error amplifier 46. The power limiting signal PWRM is supplied
to the error amplifier 46 via an input/output terminal P21 coupled
to the third terminal P13 of the main device 31. The error
amplifier 46 amplifies a difference between the power detection
signal PWRO and the power limiting signal PWRM to produce an error
voltage.
[0042] In the battery detection circuit 34 according to the present
embodiment, the error voltages corresponding to the four detected
signals are produced by the three error amplifiers 43, 44, and 46.
Typically, error amplifiers are arranged corresponding to each
detected signal. According to the present embodiment, however, the
error voltage with respect to the current Iout flowing in the
resistor R1 and the error voltage with respect to the charging
current Ichg corresponding to the battery BT are both produced by
the error amplifier 43. Thus, the number of external components for
the chip is reduced, that is, the number of external terminals is
reduced, so the size of the chip and the size of a package in which
the chip is sealed may be reduced.
[0043] As further shown in FIG. 4, the cathodes of diodes D11, D12,
and D13 are coupled to the output terminals of the error amplifiers
43, 44, and 46, respectively. The anodes of the diodes D11 to D13
are coupled to each other and also coupled to a current-voltage
conversion circuit 47. The diodes D11 to D13 transmit to the
current-voltage conversion circuit 47 a current (error current)
corresponding to the highest error voltage of the error voltages
output from the error amplifiers 43, 44, and 46. This is one of the
detected values which corresponds to the largest error.
[0044] As further illustrated in FIG. 4, a control terminal (gate)
of a transistor T21 included in a constant current source (current
control circuit) is coupled to an output terminal of the
current-voltage conversion circuit 47. The current-voltage
conversion circuit 47 supplies a signal of a voltage proportional
to the amount of current to the gate of the transistor T21.
According to the present embodiment, the transistor T21 is a
p-channel MOS transistor. The drive voltage VDC is supplied to the
source of the transistor T21, and the drain is coupled via the
input/output terminal P21 of the package including the battery
detection circuit 34 to the third terminal P13 of the main device
31.
[0045] As further illustrated in FIG. 4, the transistor T21 works
as a resistor having a resistance value dependent on a voltage
supplied to the gate thereof, and produces control current Isc
dependent on the resistance value. The transistor T21, formed of a
p-channel MOS transistor, exhibits a large resistance value for a
high gate voltage, but exhibits a small resistance value for a low
gate voltage. Consequently, as the output voltage of the
current-voltage conversion circuit 47 increases, that is, the error
that is the detection result increases, the transistor T21 reduces
control current Isc; but as the output voltage of the
current-voltage conversion circuit 47 decreases, that is, the error
being the detection result decreases, the transistor T21 increases
control current Isc.
[0046] As further illustrated in FIG. 4, when the battery BT is not
mounted in the main device 31, the battery terminal voltage VBATT
input to the error amplifier 44 is zero. Furthermore, the charging
current detected by the error amplifier 43 is also zero.
Consequently, the error is large, so the input current of the
current-voltage conversion circuit 47 is large. In this case, the
control current Isc flowing in the transistor T21 is small, so the
voltage control circuit 23 of the AC adaptor 21 outputs a lower
adaptor voltage VAC. In this state, when the battery BT is mounted,
the difference between the terminal voltage of the battery BT and
adaptor voltage VAC supplied from the AC adaptor 21 is small, so
inrush current to the battery BT is suppressed.
[0047] As further illustrated in FIG. 4, a monitoring circuit 48 is
coupled to the input/output terminal P21 of the battery detection
circuit 34. A power limiting signal PWRM output from the AC adaptor
21 illustrated in FIG. 3 is supplied via the input/output terminal
P21 from the third terminal P13 of the main device 31 to the
input/output terminal P21. The monitoring circuit 48 monitors a
voltage of the terminal P13, monitors a voltage of the input/output
terminal P21, and produces an adaptor detection signal S3
corresponding to the monitoring result.
[0048] As further illustrated in FIG. 4, the monitoring circuit 48
includes an operational amplifier 49, voltage divider circuit 50,
comparators 51 and 52, and a NAND circuit 53. A non-inverted input
terminal of the operational amplifier 49 is coupled to the
input/output terminal P21, and an output signal of the operational
amplifier 49 is fed back to an inverted input terminal thereof. The
voltage divider circuit 50 is coupled to an output terminal of the
operational amplifier 49. The voltage divider circuit 50 includes
resistors R11 and R12 coupled in series, and produces a voltage
obtained by dividing the output voltage of the operational
amplifier 49 according to the resistance values of the resistors
R11 and R12. This divided voltage is supplied to an inverted input
terminal of the comparator 51 and a non-inverted input terminal of
the comparator 52.
[0049] A reference voltage (comparison reference voltage) E1 is
input to a non-inverted input terminal of the comparator 51., and a
reference voltage (comparison reference voltage) E2 is input to an
inverted input terminal of the comparator 52. The comparators 51
and 52 are both a Schmitt Trigger comparator. The comparators 51
and 52 compare the divided voltage with reference voltages E1 and
E2, respectively, and output a signal of a level corresponding to
the comparison result.
[0050] As further illustrated in FIG. 4, the NAND circuit 53
calculates a negative AND of the output signals of the comparators
51 and 52, and thereby produces an adaptor detection signal S3.
[0051] As further illustrated in FIG. 4, the monitoring circuit 48
monitors whether or not the voltage of the power limiting signal
PWRM is in a given range, and outputs the adaptor detection signal
S3 corresponding to the monitoring result. The range set in the
monitoring circuit 48 is used to determine whether or not an AC
adaptor coupled is suitable for the main device 31 including the
monitoring circuit 48. That is, reference voltages E1 and E2 are
set correspondingly to an AC adaptor suitable for the main device
31. The monitoring circuit 48 produces, upon the coupling of an AC
adaptor suitable for the main device 31, the adaptor detection
signal S3 of L level but produces, upon coupling of an AC adaptor
unsuitable for the main device 31, the adaptor detection signal S3
of H level.
[0052] As further illustrated in FIG. 4, a switch control circuit
54 receives the above described current detection signal S1 and
charging current detection signal S2, and also receives adaptor
detection signal S3 and battery voltage detection signal. The
battery voltage detection signal is a signal produced by a
comparator 44 based on a battery terminal voltage VBATT. The
comparator 44 compares a voltage obtained by dividing the battery
terminal voltage VBATT with a reference voltage, and produces a
battery voltage detection signal corresponding to the comparison
result. The reference voltage is set according to battery terminal
voltage VBATT when the battery BT is fully charged, for
example.
[0053] The first to third switches SW1 to SW3 are coupled to the
switch control circuit 54. The switch control circuit 54 produces
control signals SC1 to SC3 in response to the signals S1 to S4. By
way of example, after the battery BT has been fully charged, the
switch control circuit 54 produces a control signal SC3 based on
the battery voltage detection signal S4, and turns OFF the third
switch SW3. As a result, the battery BT is protected from
overcharge. By way of example, when an unsuitable AC adaptor is
coupled to the main device 31, the switch control circuit 54
produces the control signal SC1 based on the adaptor detection
signal S3, and turns OFF the first switch SW1. As a result, the
main device 31 is prevented from being damaged by coupling of the
unsuitable AC adaptor.
[0054] As further illustrated in FIG. 4, the battery detection
circuit 34 includes a setting circuit 55 that limits a current
(clamps the current value to a given value) applied to the
input/output terminal P21. According to the present embodiment, the
setting circuit 55 is coupled to the input/output terminal P21,
that is, the drain terminal of the transistor T21 that outputs the
control current Isc.
[0055] As illustrated in FIG. 5, the current-voltage conversion
circuit 47 in FIG. 4 includes transistors T31 and T32, and a
resistor R21. The transistor T31 is a p-channel MOS transistor. The
transistor T31 is coupled in current mirror form to an output
transistor T21. The drive voltage VDC is supplied to the source of
the transistor T31. The gate and drain of the transistor T31 are
coupled to each other and also coupled to the gate of the
transistor T21. Furthermore, the drain of the transistor T31 is
coupled to a transistor T32. The transistor T32 is an n-channel MOS
transistor. The drain of the transistor T32 is coupled to the
transistor T31. The gate of the transistor T32 is coupled to the
anodes of the diodes D11 to D13. The source of the transistor T32
is coupled to a first terminal of a resistor R21, and a second
terminal of the resistor R21 is coupled to a ground. The gate of
the transistor T21 is coupled to a first terminal of a switch SW5
that turns ON or OFF in response to an adaptor detection signal S3,
and a second terminal of the switch SW5 is coupled to a ground.
[0056] As further illustrated in FIG. 5, the transistor T32 works
as a resistor having a resistance value dependent on a current
(error current) flowing in the diodes D11 to D13, and produces, at
a node between the transistor T31 and transistor T32, a voltage
proportional to the error current. This node voltage is supplied to
the gate of the transistor T21. Consequently, in the
current-voltage conversion circuit 47, a signal of a voltage value
proportional to the amount of current is supplied to the gate of
the transistor T21. Then, the transistor T21 produces the control
current Isc corresponding to the voltage supplied to the gate
thereof.
[0057] As further illustrated in FIG. 5, the setting circuit 55
includes transistors T41 and T42, and a constant current source 61.
The drive voltage VDC is supplied to the source of the transistor
T41; the drain of the transistor T41 is coupled to the input/output
terminal P21; and the gate of the transistor T41 is coupled to the
gate of the transistor T42. The drive voltage VDC is supplied to
the source of the transistor T42; the gate and drain of the
transistor T42 are coupled to each other. Consequently, the
transistors T41 and T42 constitute a current mirror circuit. The
drain of the transistor T42 is coupled to the constant current
source 61.
[0058] The setting circuit 55 sends a current value equal to the
value of the current flowing in the constant current source 61.
That is, a current is supplied from the setting circuit 55 to the
input/output terminal P21 at all times. The amount of current from
the setting circuit 55 is set to a value (for example, 1 .mu.A)
which does not affect the current value of control current Isc or
the voltage value of power limiting signal PWRM.
[0059] Consequently, the potential of the input/output terminal P21
when the transistor T21 coupled parallel to the setting circuit 55
is in an OFF state, is the level of the drive voltage VDC. The
potential of the input/output terminal P21 stabilizes the operation
of the battery detection circuit 34. The operation mechanism will
be described in detail.
[0060] As further illustrated in FIG. 5, in the battery detection
circuit 34, the transistor T21 is controlled so that control
current Isc flows according to the output voltages of the error
amplifiers 43, 44, and 46, that is, according to the detected
objects (the output current Iout, the charging current Ichg, the
terminal voltage of the battery BT, and the voltage across the
resistor R1). In a battery detection circuit not including the
setting circuit 55, when the DC plug 90 (refer to FIG. 1) is
inserted, during a period from the time the power source terminals
P1 and P2 of the DC plug 90 are coupled to the power source
terminals P11 and P12 of the main device 31 to the time the control
terminals P3 and P13 of the two devices are coupled, the control
terminal P13 (input/output terminal P21) is in a floating state.
Consequently, the potential of the input/output terminal P21 is the
level of the drive voltage VDC.
[0061] The monitoring circuit 48 determines that an unsuitable AC
adaptor has been coupled and outputs the adaptor detection signal
S3 corresponding to the determination result, so the switch control
circuit 54 turns OFF the switches SW2 and SW3 in response to the
adaptor detection signal S3. Furthermore, the switch SW5 turns ON
in response to the adaptor detection signal S3. Then, the
transistor T32 of the current-voltage conversion circuit 47 turns
OFF and current does not flow to the transistor T31. As a result,
current does not flow to the transistor T21, that is, the
transistor T21 turns OFF. Then, the potential of the input/output
terminal P21 lowers due to leak current. When the potential of the
input/output terminal P21 becomes lower than a threshold voltage of
the monitoring circuit 48, the monitoring circuit 48 may determine
that a suitable AC adaptor has been coupled, that is, may make an
erroneous determination, and may output the adaptor detection
signal S3 corresponding to the determination result, so the switch
control circuit 54 may turn ON the switches SW2 and SW3 in response
to the adaptor detection signal S3. Furthermore, the switch SW5
turns OFF in response to the adaptor detection signal S3. Then, in
the battery detection circuit 34, the transistor T21 is controlled
so that control current Isc flows according to the output voltages
of the error amplifiers 43, 44, and 46.
[0062] As shown in FIG. 7, the potential of the input/output
terminal P21 rises and falls in a repeating manner. The monitoring
circuit 48 erroneously determines, based on the potential of the
input/output terminal P21, that a suitable AC adaptor has not been
coupled. In the battery detection circuit 34, the transistor T21
turns ON and OFF in a repeating manner, and the switches SW2 and
SW3 also turn ON and OFF in a repeating manner. Such repeating
operation continues until the control terminals P3 and P13 are
coupled. That is, the potential of the input/output terminal P21
becomes unstable.
[0063] According to the present embodiment, in the battery
detection circuit 34, the switch SW5 is turned ON in response to
the adaptor detection signal S3, and thus the transistor T21 turns
OFF. In this case, the potential of the input/output terminal P21
becomes the level of the drive voltage VDC due to the current
produced by the setting circuit 55. Since the setting circuit 55
sends the current, the potential of the input/output terminal P21
is kept at the level of the drive voltage VDC. The monitoring
circuit 48 determines that an unsuitable AC adaptor has been
coupled, and continuously outputs adaptor detection signal S3
corresponding to the determination result, and the switch control
circuit 54 turns OFF the switches SW2 and SW3 in response to the
adaptor detection signal S3. As a result, system voltage VS
supplied from the AC adaptor to the converter 32 illustrated in
FIG. 2 changes to zero.
[0064] When the control terminals P3 and P13 are coupled to each
other with a suitable AC adaptor 21, the potential of the terminal
P21 falls due to a load provided in the AC adaptor 21, and the
voltage level of the power limiting signal PWRM supplied from the
AC adaptor 21 is provided. Then, since the potential of the
terminal P21 becomes lower than a reference voltage E2, the
monitoring circuit 48 outputs the adaptor detection signal S3 of
level H. Then, the switch SW5 turns OFF, and the transistor T21
sends the control current Isc in response to the output voltages of
the error amplifiers 43, 44, and 46. The switch control circuit 54
turns ON the switches SW1 and SW2 in response to the adaptor
detection signal S3. As a result, voltage regulated by the AC
adaptor 21 is supplied to the main device 31.
[0065] When an unsuitable AC adaptor is coupled to the main device
31, the battery detection circuit 34 similarly repeats the
operation. In this case, in the battery detection circuit 34, the
switch SW1 may be turned OFF after the time to fully insert the DC
plug, or a longer time, has elapsed, for example.
[0066] As described above, the present embodiment has the following
advantageous effects.
[0067] (1) The AC adaptor 21 produces a direct-current adaptor
voltage VAC, and varies the adaptor voltage VAC in response to the
control current Isc and outputs the power limiting signal PWRM. The
main device 31 includes the power source terminals P11 and P12,
through which the adaptor voltage VAC produced by the AC adaptor 21
is input to the main device 31, and the control terminal P13,
through which the power limiting signal PWRM is input to the main
device 31. The main device 31 includes the system circuit 33 that
operates based on adaptor voltage VAC input via the power source
terminals P11 and P12, and the battery detection circuit 34 that
detects the adaptor voltage VAC and the current Iout corresponding
to the adaptor voltage VAC by use of the resistor R1 coupled
between the power source terminal and system circuit. The battery
detection circuit 34 produces an error signal corresponding to a
difference between the adaptor voltage VAC as well as the current
Iout and the comparison reference voltage; controls the transistor
T21 based on the error signal; and supplies the control current Isc
via the control terminal P13 (input/output terminal P21) to the AC
adaptor 21. The monitoring circuit 48 compares a voltage
proportional to the potential of the control terminal P13
(input/output terminal P21) to a reference voltage, and produces,
based on the comparison result, the adaptor detection signal S3
indicating whether or not the adaptor coupled to the main device 31
is suitable for the main device 31. The switch control circuit 54
turns ON/OFF, based on the adaptor detection signal S3, the switch
SW2 coupled between the power source terminal P11 and resistor R1.
The setting circuit 55 sets the potential of the control terminal
P13 (input/output terminal P21) to a given level.
[0068] The battery detection circuit 34 of the electronic device
produces an error signal dependent on a difference between the
detected adaptor voltage VAC as well as the detected current Iout
and a comparison reference voltage, and supplies the control
current Isc, which is produced based on the error signal, via the
control terminal P13 (input/output terminal P21) to the AC adaptor
21. Also, the battery detection circuit 34 monitors a potential of
the control terminal P13 (input/output terminal P21), and
determines, based on the potential of the control terminal P13
(input/output terminal P21), whether or not an AC adaptor 21
suitable for the main device has been coupled to the main device.
If the AC adaptor 21 is not suitable, the switch SW2 is turned OFF.
The potential of the control terminal P13 (input/output terminal
P21) is set to a given level by the setting circuit 55, so that in
case the adaptor voltage VAC is supplied from the AC adaptor 21 and
the control terminal is still not coupled, the potential of the
control terminal P13 (input/output terminal P21) is suppressed from
varying in response to the control current Isc, thus stabilizing
the operation of the AC adaptor 21 when the AC adaptor 21 is being
coupled to the main device 31.
[0069] (2) The setting circuit 55, coupled to the input/output
terminal P21, is a constant current circuit which supplies constant
current to the input/output terminal P21. Consequently, the
potential of the input/output terminal P21, that is, the control
terminal P13 is clamped to a given level with a simple
configuration.
[0070] The above described embodiment may be implemented according
to the following aspect.
[0071] According to the present embodiment, the setting circuit 55
is coupled to the input/output terminal P21, that is, to the drain
terminal of the transistor T21 outputting the control current Isc.
However, the coupling points of the current control circuit and the
circuit configuration are not limited to those of the above
embodiment.
[0072] By way of example, as shown in FIG. 8, a setting circuit 55a
of a battery detection circuit 34a may be coupled to the input side
of the current-voltage conversion circuit 47, that is, coupled
between the current-voltage conversion circuit 47 and the diodes D1
to D3. The setting circuit 55a includes a switch SW11 and a
capacitor C11. A first terminal of the switch SW11 is coupled to
the anodes of the diodes D11 to D13; a second terminal of the
switch SW11 is coupled to the gate of a transistor T32 included in
the current-voltage conversion circuit 47 and a first terminal of
the capacitor C11; and a second terminal of the capacitor C11 is
coupled to the ground.
[0073] The adaptor detection signal S3 is supplied to the control
terminal of the switch SW11. The switch SW11 turns OFF in response
to the adaptor detection signal S3 (of level L in the circuit
configuration illustrated in FIG. 4) when the coupling of an AC
adaptor unsuitable for the main device 31 has been detected. The
capacitor C11 holds a gate voltage of the transistor T32 when the
switch SW11 turns OFF. Accordingly, the transistor T21 sends a
current dependent on the voltage held by the capacitor C11.
[0074] As further shown in FIG. 8, when the monitoring circuit 48
detects that an AC adaptor suitable for the main device 31 has been
coupled to the main device 31, the setting circuit 55a turns ON the
switch SW11 in response to the adaptor detection signal S3. As a
result, an error current flowing in the diodes D11 to D13 is
transmitted to the gate of the transistor T32 included in the
current-voltage conversion circuit 47. Accordingly, he transistor
T21 sends a control current Isc corresponding to the error
current.
[0075] Meanwhile, when the monitoring circuit 48 detects that an AC
adaptor suitable for the main device 31 has been coupled to the
main device 31, the setting circuit 55a turns off the switch SW11
in response to the adaptor detection signal S3. As a result, since
the capacitor C11 holds a voltage just before the switch SW11 turns
OFF, the transistor T21 sends the control current Isc corresponding
to the error current. Accordingly, the potential of the
input/output terminal P21 is equal to the level of the drive
voltage VDC.
[0076] As shown in FIG. 9, by way of example, a setting circuit 55b
of a battery detection circuit 34b may coupled to the input side of
the current-voltage conversion circuit 47, that is, coupled between
the current-voltage conversion circuit 47 and the diodes D11 to
D13. The setting circuit 55b includes two switches SW21 and SW22,
and an inverter circuit 62. A first terminal of the switch SW21 is
coupled to the anode of the diodes D11 to D13; and a second
terminal of the switch SW21 is coupled to the gate of a transistor
T32 included in the current-voltage conversion circuit 47. The
drive voltage VDC is supplied to a first terminal of the switch
SW22; a second terminal of the switch SW22 is coupled to the gate
of the transistor T32 included in the current-voltage conversion
circuit 47. The adaptor detection signal S3 is supplied to a
control terminal of the first switch SW21. An output signal of the
inverter circuit 62 which receives adaptor detection signal S3 is
supplied to a control terminal of the switch SW22. Consequently,
the first switch SW21 and second switch SW22 turn ON/OFF
alternately in response to the adaptor detection signal S3.
[0077] As further shown in FIG. 9, in the setting circuit 55b, when
the monitoring circuit 48 detects that an AC adaptor suitable for
the main device 31 has been coupled to the main device 31, the
first switch SW21 turns ON and the second switch SW22 turns OFF in
response to the adaptor detection signal S3. As a result, the
setting circuit 55b transmits an error current flowing in the
diodes D11 to D13 to the gate of the transistor T32 included in the
current-voltage conversion circuit 47. Accordingly, the transistor
T21 sends a control current Isc corresponding to the error
current.
[0078] Meanwhile, in the setting circuit 55b, when the monitoring
circuit 48 detects that an AC adaptor suitable for the main device
31 has been coupled to the main device 31, the first switch SW21
turns OFF and the second switch SW22 turns ON in response to the
adaptor detection signal S3. As a result, the drive voltage VDC is
supplied to the gate of the transistor T32. Accordingly, the
transistor T21 turns ON, so the potential of the input/output
terminal P21 is substantially equal to the level of the drive
voltage VDC.
[0079] As illustrated in FIG. 10, as another example, a setting
circuit 55c of the battery detection circuit 34b may be coupled to
the input side of the current-voltage conversion circuit 47, that
is, coupled between the current-voltage conversion circuit 47 and
the diodes D1 to D3. The setting circuit 55c includes two switches
SW31 and SW32, an inverter circuit 62, a transistor T51, and a
constant current source 71. A first terminal of the switch SW31 is
coupled to anodes of diodes D11 to D13, and a second terminal of
the switch SW31 is coupled to the gate of a transistor T32 included
in the current-voltage conversion circuit 47. A first terminal of
the switch SW32 is coupled to the gate of a transistor T51, and a
second terminal of the switch SW32 is coupled to the gate of a
transistor T32 included in the current-voltage conversion circuit
47. The transistor T51 is the similar channel-type MOS transistor
as the transistor T32. The source of the transistor T51 is coupled
to the ground and the drain is coupled to the constant current
source 71. Further, the gate of the transistor T51 is coupled to
the drain. Thus, the transistors T32 and T51 constitute a current
mirror circuit when the switch SW32 turns ON, and the current
proportional to the current value of the constant current source 71
flows to the transistor T32.
[0080] As further depicted in FIG. 10, the adaptor detection signal
S3 is supplied to a control terminal of the first switch SW31. An
output signal of the inverter circuit 62, to which the adaptor
detection signal S3 is input, is supplied to a control terminal of
the second switch SW32. Thus, the first switch SW31 and the second
switch SW32 alternately turn ON/OFF in response to the adaptor
detection signal 53.
[0081] In the setting circuit 55c of FIG. 10, when the monitoring
circuit 48 detects that an AC adaptor suitable for the main device
31 has been coupled to the main device 31, in response to the
adaptor detection signal S3, the first switch SW31 turns ON and the
second switch SW32 turns OFF. As a result, the setting circuit 55c
transmits the error current which flows to the diodes D11 to D13 to
the gate of the transistor T32 included in the current-voltage
conversion circuit 47. Accordingly, the transistor T21 sends
control current Isc corresponding to the error current.
[0082] Meanwhile, in the setting circuit 55c, when the monitoring
circuit 48 detects that an AC adaptor unsuitable for the main
device 31 has been coupled to the main device 31, in response to
the adaptor detection signal S3, the first switch SW31 turns OFF
and the second switch SW32 turns ON. As a result, the setting
circuit 55c supplies a gate voltage of the transistor T51 to the
gate of the transistor T32. The transistor T32 sends current
proportional to the current sent by the constant current source 71.
Accordingly, constant current flows into the transistor T21, and
the potential of the input/output terminal P21 becomes the level of
the drive voltage VDC.
[0083] The above described embodiment is implemented by using the
error amplifier 43 which compares two input signals with a
reference voltage and outputs an error voltage. However, the
embodiment may be implemented by using an error amplifier which
compares three or more input signals with a reference voltage and
outputs an error voltage. Furthermore, the terminal
inversion/non-inversion may be varied appropriately.
[0084] According to the above described embodiments, in the battery
detection circuit 34 illustrated in FIG. 4, a voltage (output
voltage) at the output side terminal of the resistor R1 is
detected, but this may be omitted. For example, the embodiments may
be implemented by using a battery detection circuit in which the
multiplier 45, the error amplifier 46, and the diode D13 are
omitted.
[0085] According to the above described embodiments, the adaptor
voltage VAC is regulated in proportion to the control current Isc.
However, the relationship between the control current Isc and the
adaptor voltage VAC may be varied appropriately.
[0086] According to the above described embodiments, the power
limiting signal PWRM is output from the pulse width modulator 24.
However, the power limiting signal PWRM may be output from a
circuit other than the pulse width modulator 24. For example, a
circuit such as a register which outputs the power limiting signal
PWRM may be coupled to the third terminal P3 acting as the control
terminal.
[0087] The battery detection circuit of the electronic device
produces an error signal corresponding to a difference between a
detected adaptor voltage as well as an adaptor current and a
comparison reference voltage, and supplies a control current
produced based on the error signal via the control terminal to the
external power source. Also, the battery detection circuit monitors
a potential of the control terminal, and determines, based on the
potential of the control terminal, whether or not an external power
source suitable for the main device has been coupled to the main
device, and if not, turns OFF the switch. The potential of the
control terminal is set to a given level by the setting circuit.
Thus, when an adaptor voltage is supplied from the external power
source and the control terminal is still not coupled, the potential
of the control terminal is suppressed from varying in response to
the control current, so the operation is stabilized when the
external power source is coupled.
[0088] According to the above described embodiments, the operation
is stabilized when an external power source is coupled.
[0089] Numbers applied to the embodiments (first, second or third
etc.) do not show priorities of the embodiments. Many variations
and modifications will be apparent to those skilled in the art.
[0090] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority and
inferiority of the invention. Although the embodiments of the
present inventions have been described in detail, it should be
understood that the various changes, substitutions, and alterations
could be made hereto without departing from the spirit and scope of
the invention.
* * * * *